Perfume for genes

The sea and Homer are moving love, evolution - sexual selection. Males most attractive for females can strengthen their reproductive success, and females improve the quality of offspring, choosing partners with good genes. The possibility of choice is a great good, but at the same time a great risk. Indeed, usually the female compares partners on indirect features, for example, by the size of horns or the quality of the nest, and may be mistaken. But there are species among animals in which the competition and the choice of genes occur in almost its pure form: males leave sperm in an accessible place, females use or reject it, but do not see the manufacturer.

The species that distribute sex products in this way include colleps Orchesella cincta , tiny arthropods living in soil litter. These creatures attracted the attention of the employees of the University of Amsterdam (VU University Amsterdam) under the leadership of Professor Yazintha Euers, who were interested in the female collebox, choosing material for fertilization among a large number of samples. It turned out that the conditions in which this sample was left.

Scientists worked with collembols, which were bred in the laboratory. The period of puberty in males in laboratory conditions lasts five days. At this time, they leave droplets of sperm (spermatophores) and experience one molting. Although Orchensella males do not enter into direct struggle with rivals, other people's spermatophores can ruin or even gobble up. Where colleps live, spermatophores are scattered densely, but the female takes only one. Researchers were interested in whether the number of spermatophores left by the male depends on the presence of competitors, and whether females make a choice or take the first sample that came across.

At the first stage, they watched 71 a male and calculated how many spermatophores each of them would leave to molting. It turned out that the number of droplets varies from 238 to 7. After molting, males were divided into three groups. Each was placed in a plastic cup with a diameter of 5 cm, divided into two parts with a small mesh. In one half of her, the male Orchella put off his spermatophores, the other half was empty or there was another male, or an adult, but not yet reaching puberty, or quite sexually mature. Through the grid, the neighbors did not see each other, but tossed. It turned out that the males who put off spermatophores next to the opponent, no matter whether it was sexually mature or not, significantly reduced their number compared to the first masonry. In the control group, there was practically no difference between the first and second times.

Then it was the turn of females to make a choice. They were once placed in a cup, on one half of which there were two spermatophores of control males, and on the other two spermatophores laid in the presence of the opponent. The female was given a choice of 15 minutes, during this time 24 colleboles out of 40 were determined, of which only 6 preferred spermatofor of control males, the rest chose sex products produced in conditions of competition.

The fact that the experimental colleboles do not pay attention to the neighbor's puberty is understandable: males Orchesella , adults, but still unable to postpone their own spermatophores, are already spoiling strangers with might and main. It is more amazing that in conditions of competition, males do not increase the amount of ejaculate (let the opponent choke!), And reduce it. As for other species, usually in conditions of competition, males increase sperm products, most rodents, for example, do so, but house mice, on the contrary, reduce the volume of ejaculate to cope as quickly as possible.

Although in the presence of rivals colletmobol Orchesella will produce fewer spermatophores, they manage to make them more attractive to females. Obviously, spermatophores have distinct markers indicating the expected advantages. Based on observations that they do not describe, the researchers suggested that females choose by smell.

Males are able to synthesize a bouquet of pheromones, which changes depending on the situation. But in conditions when the densatophore density is high, the female is difficult to correlate a certain smell with a specific drop. In this case, it is preferable that the signal is stronger, but its synthesis may be more “more expensive”. Therefore, a reduction in the number of spermatophores is an optimizing strategy. Process a relatively small amount of sexual products with attractive label for males. They prefer to win not in number, but in quality.

Researchers came to the conclusion that males Orchesella make their genes attractive to the female, changing the chemical mark depending on the level of competition. This is a preliminary conclusion, the label still needs to be characterized. Perhaps females make their choice in this way in a wider range of taxa.

1. ZV ZIZZARI, NM Van Straalen, J. Ellers. Male-Male Competition Leads to Less Abundant But More Attractive Sperm, Biol. Lett 9: 20130762 (2013)